1. Field of the Invention
The present invention relates to an automotive vehicle in which the center position of a center bearing of a propeller shaft assembly is variable relative to the vehicle body, and more particularly to a system for reducing vibration and noise due to secondary couple generated with angles of cardan joints upon vehicle starting.
2. Description of the Prior Art
There is shown, by way of example, a propeller shaft of the prior art in FIG. 7a, in which reference numerals 1 and 2 denote a first propeller shaft and a second propeller shaft of a propeller shaft assembly, respectively, and 3, 4 and 5 denote cardan joints (referred to hereinafter as first, second and third cardan joints) which swingably connect a main shaft or a transmission output shaft 6 with the first propeller shaft 1, the first propeller shaft 1 with the second propeller shaft 2 and the second propeller shaft 2 with a drive pinion of a differential 7. A center bearing 8 is fixed near the middle position of the shaft total length obtained by adding the length of the first propeller shaft 1 to that of the second propeller shaft 2. As seen from an enlarged detail show in FIG. 7b, the center bearing 8 is supported by an upper bracket 11 connected to a vehicle body through a cushion rubber layer 10. A lower bracket 12 is connected to the upper bracket 11 by means of a bolt. With this propeller shaft, when vibration is transmitted to the first and second propeller shafts 1, 2 from the main shaft 6 and the differential 7, the propeller shaft 1 moves up and down in a movable area defined by the center bearing 8 and the upper and lower brackets 11, 12, which are cushioned by an insulator 9 and the cushion rubber layer 10. A vehicle having this 3-joint type propeller shaft was good noise characteristics at a high speed and critical engine speed performance compared with a vehicle having a 2-joint type propeller shaft, so that the 3-joint type propeller shaft is frequently used in small vehicles in recent years.
The 3-joint type propeller shaft offers the above-mentioned advantages, but this propeller shaft is worse than the 2-joint type propeller shaft in respect to vibration and noise due to secondary couple generated with angles of cardan joints during vehicle starting when there occurs wind-up of the differential. That is, with the 2-joint type, the above-mentioned vibration and noise can be reduced by arranging the main shaft and the differential on the same straight line to provide a drive system in which variations in exciting force become small when there occurs wind-up of the differential. On the other hand, with the 3-joint type, the propeller shaft is fixed to the vehicle body by the center bearing so that a certain angle is inevitably formed between the main shaft and the differential. Specifically, during vehicle starting where there are great variations the propeller shaft torque, which is proportional to input torque, the insulator and the cushion rubber are not sufficient for preventing the above-mentioned vibration and resultant noise.
It is therefore an object of the present invention to provide a system for reducing vibration and noise derived from a drive system of an automotive vehicle owing to a propeller shaft assembly.